Front structure of vehicle body

ABSTRACT

A front portion of a vehicle body includes front side frames, a subframe, and a vehicle compartment front structure body. The subframe has a subframe body and a pair of rear fastening portions fastened to a vehicle compartment front structure body in left and right rear regions of the subframe body. The rear fastening portion has a tubular body through which a bolt penetrates in a vertical direction, and a convex portion protruding from the tubular body toward a vehicle rear side. The vehicle compartment front structure body has a support plate extending substantially horizontally in which the tubular body is fastened to a lower surface of the support plate by the bolt, and a fall restricting wall facing the convex portion from the vehicle rear side at a position rearward of a fastening portion of the support plate fastened with the bolt.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefits of Japanese application no. 2020-215298, filed on Dec. 24, 2020. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND Technical Field

The disclosure relates to a front structure of a vehicle body.

Description of Related Art

A structure of a front portion of a vehicle body is known, in which a dash lower panel that separates between a vehicle compartment and an engine room is provided with an inclined wall that inclines downward toward the vehicle rear side, and when an impact load is input from the front of the vehicle, mounted components that move rearward are dropped downward along the inclined wall (see Patent Document 1, for example).

In the front structure of the vehicle body described in Patent Document 1, an auxiliary plate is attached to the front surface side of the inclined wall of the dash lower panel, and a drive device such as an engine is arranged on the front side of the auxiliary plate. In this front structure of the vehicle body, when an impact load is input from the front of the vehicle and causes the drive device to come into contact with the auxiliary plate, the auxiliary plate is separated from the dash panel and the auxiliary plate, together with the drive device, falls downward along the inclined wall of the dash panel.

RELATED ART Patent Document

[Patent Document 1] Japanese Patent No. 2855411

Problems to be Solved

The front structure of the vehicle body described in Patent Document 1 can drop the drive device downward when an impact load is input from the front of the vehicle to prevent entry of the drive device in the direction into the vehicle compartment. However, for many vehicles in recent years, a subframe is arranged on the rear side of the engine (drive device), and steering components and suspension components are supported by the subframe. In such vehicles, the structure described in Patent Document 1 cannot be adopted.

The subframe arranged in the engine room is erected below the left and right front side frames, and the rear end side portion thereof is supported by a vehicle compartment front structure body in front of the vehicle compartment. In the case of such a front structure of the vehicle body, it is desired to smoothly drop the rigid subframe downward on the front side of the vehicle compartment when an impact load is input from the front of the vehicle.

As a countermeasure, it is known to provide a support plate having a relatively low rigidity and extending substantially horizontally in the vehicle compartment front structure body, and fasten a rear fastening portion of the subframe to the lower surface of the support plate with a bolt. In this case, when an impact load is input from the front of the vehicle and causes the subframe to be pressed to the rear of the vehicle, the bolt fastening portion of the support plate breaks, so that the rear portion of the subframe falls downward on the front side of the vehicle compartment.

However, since the rear fastening portion of the subframe is bolted to the lower surface of a support wall that has a relatively low rigidity, it is conceivable that depending on the input direction of the load applied to the subframe, the support wall may have out-of-plane deformation toward the upper side, and the bolt fastening portion may not be broken smoothly.

SUMMARY

A front structure of a vehicle body according to the disclosure adopts the following configuration. That is, the front structure of the vehicle body according to the disclosure includes: a pair of left and right front side frames (for example, the front side frames 7 of the embodiment) extending to a front of a vehicle on a front side of a vehicle compartment; a subframe (for example, the subframe 8 of the embodiment) erected below the pair of front side frames; and a vehicle compartment front structure body (for example, the vehicle compartment front structure body 30 of the embodiment) arranged in a front portion of the vehicle compartment. The subframe includes: a subframe body (for example, the subframe body 41 of the embodiment) supporting a mounted component; and a rear fastening portion (for example, the rear fastening portion 35 of the embodiment) fastened to the vehicle compartment front structure body in a rear region of the subframe body. The rear fastening portion includes: a tubular body (for example, the tubular body 45 of the embodiment) through which a bolt (for example, the bolt 15 of the embodiment) penetrates in a vertical direction; and a convex portion (for example, the convex portion 46 of the embodiment) which protrudes from the tubular body to a vehicle rear side. The vehicle compartment front structure body includes: a support plate (for example, the support plate 14 of the embodiment) extending substantially horizontally in which the tubular body is fastened to a lower surface of the support plate by the bolt; and a fall restricting wall (for example, the inclined wall 20 of the embodiment) which faces the convex portion from the vehicle rear side at a position rearward of a fastening portion of the support plate fastened with the bolt and against which the convex portion is pressed when an impact load is input from the front of the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the front portion of the vehicle of the embodiment.

FIG. 2 is a partial cross-sectional perspective view of the front portion of the vehicle of the embodiment.

FIG. 3 is a bottom view of the front portion of the vehicle of the embodiment.

FIG. 4 is a perspective view, corresponding to the arrow view IV of FIG. 1 , of the front portion of the vehicle of the embodiment.

FIG. 5 is a partial cross-sectional side view of the front portion of the vehicle corresponding to the cross section V-V of FIG. 3 of the embodiment.

FIG. 6 is a left side view of the front portion of the vehicle of the embodiment.

FIG. 7 is an enlarged view of the part VII of FIG. 4 of the front portion of the vehicle of the embodiment with some components removed.

FIG. 8 is a perspective view of viewing substantially the same portion as FIG. 7 of the front portion of the vehicle of the embodiment from another angle.

FIG. 9 is an enlarged view of the part IX of FIG. 4 of the front portion of the vehicle of the embodiment with some components removed.

FIG. 10 is an enlarged view of the part X of FIG. 5 of the vehicle of the embodiment.

FIG. 11 is a perspective view, corresponding to the arrow view XI of FIG. 5 , of the front portion of the vehicle of the embodiment.

FIG. 12 is a partial cross-sectional side view similar to FIG. 6 showing the deformation behavior of the front portion of the vehicle of the embodiment.

FIG. 13 is a partial cross-sectional side view similar to FIG. 6 showing the deformation behavior of the front portion of the vehicle of the embodiment.

FIG. 14 is a partial cross-sectional side view similar to FIG. 6 showing the deformation behavior of the front portion of the vehicle of the embodiment.

FIG. 15 is a partial cross-sectional side view similar to FIG. 6 showing the deformation behavior of the front portion of the vehicle of the embodiment.

FIG. 16 is a partial cross-sectional side view similar to FIG. 6 showing the deformation behavior of the front portion of the vehicle of the embodiment.

FIG. 17 is a partial cross-sectional side view similar to FIG. 6 showing the deformation behavior of the front portion of the vehicle of the embodiment.

FIG. 18 is a partial cross-sectional side view similar to FIG. 6 showing the deformation behavior of the front portion of the vehicle of the embodiment.

DESCRIPTION OF THE EMBODIMENTS

The disclosure provides a front structure of a vehicle body that can more smoothly drop the subframe downward when an impact load is input from the front of the vehicle.

Means for Solving the Problems

A front structure of a vehicle body according to the disclosure adopts the following configuration. That is, the front structure of the vehicle body according to the disclosure includes: a pair of left and right front side frames (for example, the front side frames 7 of the embodiment) extending to a front of a vehicle on a front side of a vehicle compartment; a subframe (for example, the subframe 8 of the embodiment) erected below the pair of front side frames; and a vehicle compartment front structure body (for example, the vehicle compartment front structure body 30 of the embodiment) arranged in a front portion of the vehicle compartment. The subframe includes: a subframe body (for example, the subframe body 41 of the embodiment) supporting a mounted component; and a rear fastening portion (for example, the rear fastening portion 35 of the embodiment) fastened to the vehicle compartment front structure body in a rear region of the subframe body. The rear fastening portion includes: a tubular body (for example, the tubular body 45 of the embodiment) through which a bolt (for example, the bolt 15 of the embodiment) penetrates in a vertical direction; and a convex portion (for example, the convex portion 46 of the embodiment) which protrudes from the tubular body to a vehicle rear side. The vehicle compartment front structure body includes: a support plate (for example, the support plate 14 of the embodiment) extending substantially horizontally in which the tubular body is fastened to a lower surface of the support plate by the bolt; and a fall restricting wall (for example, the inclined wall 20 of the embodiment) which faces the convex portion from the vehicle rear side at a position rearward of a fastening portion of the support plate fastened with the bolt and against which the convex portion is pressed when an impact load is input from the front of the vehicle.

In the above configuration, when an impact load is input from the front of the vehicle, the subframe is pressed toward the vehicle rear side, and the convex portion protruding rearward from the rear fastening portion is pressed against the fall restricting wall. As a result, the falling of the tubular body of the rear fastening portion is restricted, and the out-of-plane deformation of the support plate is suppressed. As a result, the fastening portion of the support plate is smoothly broken by the load acting on the subframe, and the rear portion of the subframe falls downward.

The convex portion may include: a contact surface (for example, the contact surface 46 a of the embodiment) which comes into contact with the fall restricting wall when the impact load is input from the front of the vehicle; and an upper inclined surface (for example, the upper inclined surface 46 b of the embodiment) which inclines downward from an upper region of the tubular body toward the vehicle rear side and connects the upper region and the contact surface.

In this case, the contact surface is arranged in the lower region at the rear portion of the tubular body. Further, the reaction force acting on the contact surface from the fall restricting wall is efficiently transmitted to the tubular body through a portion having a vertical height that gradually increases toward the root portion side (the side of the tubular body) of the upper inclined surface. Accordingly, when this configuration is adopted, the falling of the tubular body of the rear fastening portion can be more reliably restricted.

A reinforcing member (for example, the reinforcing plate 48 of the embodiment) having a high rigidity may be attached to a rear surface side of the fall restricting wall, and a reinforcing convex portion (for example, the reinforcing convex portion 51 of the embodiment) that bulges toward a vehicle front side may be provided at a position rearward of a portion on the fall restricting wall, with which the contact surface of the convex portion comes into contact when the impact load is input from the front of the vehicle, of the reinforcing member.

In this case, when the contact surface of the convex portion of the rear fastening portion is pressed against the fall restricting wall at the time of input of an impact load from the front of the vehicle, the reinforcing convex portion of the reinforcing member arranged on the rear side takes the pressing load thereof. As a result, the reaction force quickly acts on the contact surface of the convex portion, and the falling of the tubular body of the rear fastening portion is reliably restricted.

The reinforcing member may have an upper joint portion (for example, the upper joint portion 48 a of the embodiment) joined to an upper surface of the support plate. A fixing nut (for example, the fixing nut 17 of the embodiment) constituting the fastening portion may be fixed to the upper surface of the support plate, and the upper joint portion may be formed with an elongated hole (for example, the elongated hole 49 of the embodiment) that surrounds a periphery of the fixing nut and has a gap between the upper joint portion and a rear portion of the fixing nut.

In this case, at the time of input of an impact load from the front of the vehicle, when the load toward the vehicle rear side acts on the fixing nut through the bolt along with the rear displacement of the rear fastening portion, the fixing nut is displaced toward the rear of the vehicle in the elongated hole of the reinforcing member while being pulled downward. As a result, the support plate reliably breaks and the rear portion of the subframe falls downward.

The support plate may be fixed to an edge portion of an opening (for example, the opening 50 of the embodiment) at a lower end of a mount bracket (for example, the mount bracket 13 of the embodiment) that bulges downward. A fixing nut (for example, the fixing nut 17 of the embodiment) constituting the fastening portion may be fixed to an upper surface of the support plate, and the fixing nut may be arranged close to an edge portion on a front side of the opening of the mount bracket.

In this case, the portion of the support plate on the front side of the fixing nut is supported close to the edge portion of the highly rigid opening of the mount bracket. Therefore, at the time of input of an impact load from the front of the vehicle, when the load toward the vehicle rear side acts on the fixing nut through the bolt along with the rearward displacement of the rear fastening portion, stress tends to concentrate in a narrow range on the rear side of the fixing nut of the support plate. As a result, a part of the support plate is reliably broken, and the rear portion of the subframe falls downward.

A step portion (for example, the step portion 21 of the embodiment) including a front wall (for example, the front wall 18 of the embodiment) extending downward from the lower end of the mount bracket, a substantially horizontal wall (for example, the substantially horizontal wall 19 of the embodiment) extending from a lower end of the front wall to a rear of the vehicle, and an inclined wall (for example, the inclined wall 20 of the embodiment) inclining downward from a rear end of the substantially horizontal wall toward the vehicle rear side may be provided at a rear portion of the support plate, and the inclined wall may serve as the fall restricting wall.

In this case, when an impact load is input from the front of the vehicle, the convex portion protruding from the rear fastening portion comes into contact with the inclined wall of the step portion, so that the falling of the tubular body of the rear fastening portion is restricted. Further, even if the convex portion is slightly lifted upward due to the falling load of the tubular body, the convex portion comes into contact with the substantially horizontal wall of the step portion, so that the falling of the tubular body can be reliably restricted. In addition, when the fastening plate breaks and the rear fastening portion is detached from the mount bracket, the rear fastening portion is guided by the front surface side of the step portion and smoothly falls downward.

A tunnel frame (for example, the tunnel frame 11 of the embodiment) extending in a vehicle front-rear direction may be arranged below the vehicle compartment, and the step portion may be arranged at a front end portion of the tunnel frame.

In this case, the rear fastening portion detached from the mount bracket when an impact load is input from the front of the vehicle smoothly falls downward along the step portion and the lower surface of the tunnel frame.

A steering gear box (for example, the steering gear box 40 of the embodiment) may be mounted on the subframe so as to project upward. The vehicle compartment front structure body may include a dash lower panel (for example, the dash lower panel 5 of the embodiment) that separates the vehicle compartment and a front compartment on a front side of the vehicle compartment, and an inclined guide portion (for example, the inclined guide portion 60 of the embodiment) that inclines downward toward the vehicle rear side may be provided at a position, which faces an upper portion of the steering gear box from the vehicle rear side, of the dash lower panel.

In this case, when the subframe is displaced rearward at the time of input of an impact load from the front of the vehicle, the upper portion of the steering gear box comes into contact with the inclined guide portion of the dash lower panel. At this time, the upper portion of the steering gear box is guided by the inclined guide portion, so that the subframe smoothly falls downward.

The inclined guide portion of the dash lower panel may be arranged on an inner side in a vehicle width direction of the front end portion of the tunnel frame.

In this case, when the subframe is displaced rearward at the time of input of an impact load from the front of the vehicle, the subframe stably falls downward along the inclined guide portion of the dash lower panel and the step portion at the front end of the tunnel frame.

The subframe may include a front fastening portion (for example, the front fastening portion 34 of the embodiment) fastened to the front side frame in the front region of the subframe body. A component mounting bracket (for example, the component mounting bracket 25 of the embodiment) having an inclined portion (for example, the inclined guide portion 24 of the embodiment) with a front surface that inclines downward toward the vehicle rear side may be coupled to a rear portion of the front side frame, and the inclined portion may be arranged on a track in which the front fastening portion detached from the front side frame is displaced rearward when the impact load is input from the front of the vehicle.

In this case, when an impact load is input from the front of the vehicle, the front fastening portion of the subframe is detached from the front side frame along with the bending and deformation of the front side frame, and is displaced toward the vehicle rear side. At this time, the front fastening portion comes into contact with the front surface of the inclined portion on the component mounting bracket to be guided downward by the inclined portion. As a result, the subframe is guided below the vehicle along the slope that the rear fastening portion, the steering gear box, and the front fastening portion respectively contact.

Effects

According to the disclosure, the rear fastening portion of the subframe is provided with the convex portion that protrudes from the tubular body toward the vehicle rear side, and the fall restricting wall that faces the convex portion of the rear fastening portion from the vehicle rear side is provided on the rear side of the fastening portion of the support plate of the vehicle compartment front structure body. Therefore, when an impact load is input from the front of the vehicle, the convex portion is pressed against the fall restricting wall, so that the falling of the tubular body of the rear fastening portion is restricted and the out-of-plane deformation of the support plate is suppressed. Accordingly, when the disclosure is adopted, the subframe can be dropped downward more smoothly when an impact load is input from the front of the vehicle.

Hereinafter, embodiments of the disclosure will be described with reference to the drawings. In addition, an arrow FR pointing to the front side of a vehicle, an arrow UP pointing to the upper side of the vehicle, and an arrow LH pointing to the left side of the vehicle are marked at appropriate positions in the drawings.

FIG. 1 is a perspective view of viewing the front portion of the vehicle 1 of the present embodiment from the upper left diagonally. FIG. 2 is a partial cross-sectional perspective view of cutting the front portion of the vehicle 1 at a portion slightly to the right of the center in a vehicle width direction, and viewing the portion from the rear left upper side diagonally. Further, FIG. 3 is a bottom view of the front portion of the vehicle 1. As shown in FIG. 2 , the rear end portion of a dash lower panel 5 that separates a vehicle compartment 2 and an engine room 4 (front compartment) in front of the vehicle compartment 2 is joined to the front end portion of a floor panel 3 arranged below the vehicle compartment 2. The dash lower panel 5 stands diagonally upward on the front side from the joint with the floor panel 3. Further, as shown in FIG. 3 , in the central portion of the floor panel 3 in the vehicle width direction, a floor tunnel portion 6 that bulges upward extends along a vehicle front-rear direction. The lower edge of the central region of the dash lower panel 5 in the vehicle width direction is connected to the front end portion of the floor tunnel portion 6, and the amount of bulge toward the front side is smaller than that of the other regions on the left and right.

A pair of left and right front side frames 7, which are the main skeleton members of the front portion of the vehicle body, are provided on the front side of the vehicle compartment 2. The left and right front side frames 7 extend toward the front of the vehicle on the left and right front sides of the vehicle compartment 2. A subframe 8 for supporting steering components and suspension components is erected below the left and right front side frames 7 near the rear portion. The subframe 8 is an aluminum casting having a substantially rectangular shape in the plan view, and is fixed to the left and right front side frames 7 and a vehicle compartment front structure body 30 (to be described later) by fastening bolts. A power unit (not shown) such as an engine or a drive motor is supported by a front frame portion (not shown) connected to the front portion of the subframe 8. The front frame portion is erected in the central region in the front-rear direction of the left and right front side frames 7.

FIG. 4 is a perspective view, corresponding to the arrow view IV of FIG. 1 , of the front portion of the vehicle 1. Side sills 9 (see FIG. 4 ), which are skeleton members extending along the vehicle body front-rear direction, are arranged at the lower ends on both the left and right sides of the vehicle compartment 2. Floor frames 10 extending substantially along the vehicle front-rear direction are arranged on the inner side of the left and right side sills 9 in the vehicle width direction. Further, as shown in FIG. 3 , tunnel frames 11 extending substantially along the vehicle front-rear direction are arranged between the left and right floor frames 10 and the central floor tunnel portion 6. Both the floor frame 10 and the tunnel frame 11 are formed in a hat-shaped cross-sectional shape that opens to the upper side, and the floor panel 3 is joined to the upper surfaces thereof. The floor frame 10 and the tunnel frame 11 form a closed cross section extending substantially along the vehicle front-rear direction with the floor panel 3.

As shown in FIG. 4 , the front end portion of each of the left and right side sills 9 and the front region of the adjacent floor frame 10 are connected to each other by an outrigger 12 having a closed cross-section structure. Further, the front end portion of the floor frame 10 is further curved and extends forward and upward from the portion connecting with the outrigger 12, and is connected to the rear portion of the corresponding front side frame 7 on the left and right. Therefore, the rear portions of the left and right front side frames 7 are continuous with the corresponding floor frames 10 below the vehicle compartment 2.

FIG. 5 is a partial cross-sectional side view of the front portion of the vehicle 1 corresponding to the cross section V-V of FIG. 3 , and FIG. 6 is a left side view of the front portion of the vehicle 1. Further, FIG. 7 is an enlarged view of the part VII of FIG. 4 of the front portion of the vehicle 1 with some components removed, and FIG. 8 is a perspective view of viewing substantially the same portion as FIG. 7 of the front portion of the vehicle 1 from another angle. As shown in FIG. 7 and FIG. 8 , the front region of the floor frame 10 and the front end portion of the adjacent tunnel frame 11 are connected to each other via a mount bracket 13. The mount bracket 13 is joined to the lower surface of the lower region of the rising portion of the dash lower panel 5 and forms a closed cross section with the dash lower panel 5. The end portion of the mount bracket 13 on the side of the tunnel frame 11 is joined to the tunnel frame 11 so as to surround the peripheral region of the front end portion of the tunnel frame 11 and a part of the lower surface. An opening 50 (see FIG. 11 ) is formed on the lower surface of the mount bracket 13. A support plate 14 is attached to the mount bracket 13 so as to close the opening 50 on the lower surface. The support plate 14 is formed of a metal plate having a smaller wall thickness than the mount bracket 13. A bolt insertion hole 16 is formed in the support plate 14 at a position facing the front side region of the tunnel frame 11. A bolt 15 (see FIG. 3 to FIG. 5 ) for fixing a rear fastening portion 35 (to be described later) of the subframe 8 is inserted into the bolt insertion hole 16 from below. A fixing nut 17 (see FIG. 10 and FIG. 11 ) into which the shaft portion of the bolt 15 inserted into the bolt insertion hole 16 is screwed is attached to the upper surface side of the support plate 14. Since the support plate 14 is a thin plate made of metal, when an impact load of a predetermined value or more is input from the rear fastening portion 35 of the subframe 8 through the bolt 15, the peripheral edge portion of the fixing nut 17 may break. As a result, the rear fastening portion 35 is allowed to be detached (dropped) from the mount bracket 13 (vehicle compartment front structure body 30).

Furthermore, the front edge portion of the tunnel frame 11 is stacked and joined to the rear edge portion of the mount bracket 13. As shown in FIG. 7 , at the front edge portion of the tunnel frame 11, a front wall 18 extending downward while slightly inclining to the rear side from the rear portion of the portion overlapped with the lower surface of the mount bracket 13, a substantially horizontal wall 19 extending from the lower end of the front wall 18 to the vehicle rear side, and an inclined wall 20 inclining downward from the rear end of the substantially horizontal wall 19 toward the vehicle rear side are continuously formed. The front wall 18, the substantially horizontal wall 19, and the inclined wall 20 constitute a step portion 21 at the front edge portion of the tunnel frame 11. The entire front surface of the step portion 21 inclines downward toward the vehicle rear side. The inclined portion on the front surface of the step portion 21 constitutes an inclined guide portion 33 (second inclined guide portion). The inclined guide portion 33 is arranged on a track in which the rear fastening portion 35 of the subframe 8 is displaced rearward when an impact load is input from the front of the vehicle. Further, the inclined wall 20 of the step portion 21 constitutes a fall restricting wall (to be described later).

As shown in FIG. 5 and FIG. 6 , each of the left and right front side frames 7 has a narrower vertical width on the rear end side than the vertical width on the front end side. On the lower surface near the rear portion of each front side frame 7, there is a portion where the height of the lower surface is stepped high (the vertical width narrows in a stepped manner) with respect to the substantially horizontal upper surface. The portion stepped high (the root of the portion where the vertical width narrows in a stepped manner) is a bending starting point 22 where the front side frame 7 receives a load and bends and deforms when an impact load is input from the front of the vehicle. When the front side frame 7 receives an impact load from the front side thereof, the front side frame 7 bends and deforms so that the front side of the bending starting point 22 is lifted upward with the bending starting point 22 as the center (see FIG. 17 and FIG. 18 ). Further, a mounting bracket 23 (subframe mounting portion) to which a front fastening portion 34 (to be described later) of the subframe 8 is fastened is fixed at the front side position of the bending starting point 22 on the lower surface of each front side frame 7.

In addition, a component mounting bracket 25 having an inclined guide portion 24 (inclined portion) is integrally coupled at the position rearward and downward of the bending start point 22 of each front side frame 7. As shown in FIG. 7 and FIG. 8 , the component mounting bracket 25 has a pair of side walls 25 a having a substantially triangular shape in the side view, a front wall 25 b connecting the front end portions of the pair of side walls 25 a, and a lower wall 25 c connecting the lower end portions of the pair of side walls 25 a, and the front surface side of the front wall 25 b is the inclined guide portion 24. The front surface of the inclined guide portion 24 inclines downward toward the vehicle rear side. The component mounting bracket 25 is stacked so as to cover the front edge portion of the corresponding floor frame 10 on the left and right from below, and is joined to the front edge portion of the floor frame 10 in this state.

The inclined guide portion 24 (front wall 25 b) of the component mounting bracket 25 is formed with a recessed portion 31 extending in the vertical direction. The recessed portion 31 extends from the front surface of the front wall 25 b of the component mounting bracket 25 to the front end portion of the lower surface of the lower wall 25 c. Further, a rear end joint portion 32 joined to the front surface of the inclined guide portion 24 (front wall 25 b) of the component mounting bracket 25 extends on the lower wall on the rear portion side of each front side frame 7. The rear end joint portion 32 is joined to the front surface of the inclined guide portion 24 (front wall 25 b) so as to be continuous with the upper end portion (the portion starting to be recessed rearward and downward) of the recessed portion 31.

One end portion of a mount holding plate 27 that holds a support mount 26 (see FIG. 4 ) of a suspension arm is fastened and fixed to the lower wall of the component mounting bracket 25. Reference numeral 28 in FIG. 7 and FIG. 8 is a bolt insertion hole through which a bolt 29 (see FIG. 4 ) for fixing the mount holding plate 27 to the component mounting bracket 25 is inserted. The other end portion of the mount holding plate 27 is bolted to the lower surface near the rear portion of the subframe 8. The support mount 26 is fixed to the component mounting bracket 25 and the subframe 8 so as to be sandwiched from above and below by a holding plate on the upper side (not shown) and the mount holding plate 27. The component mounting bracket 25 is formed of an aluminum casting similar to the subframe 8 or a member having a rigidity equivalent to that of the aluminum casting.

The subframe 8 includes a subframe body 41 having a substantially rectangular shape in the plan view to which the steering gear box 40 (mounted component) is attached on the upper surface on the rear portion side, a pair of leg portions 42 protruding upward from the left and right front regions of the subframe body 41, the front fastening portions 34 provided on top portions 42 a of the leg portions 42 and fastened to the corresponding front side frames 7 on the left and right, and the rear fastening portions 35 arranged in the left and right rear regions of the subframe body 41 and fastened to the lower ends (support plate 14) of the left and right mount brackets 13 described above. In the present embodiment, the mount bracket 13, the support plate 14, the component mounting bracket 25, the dash lower panel 5, etc. constitute the vehicle compartment front structure body 30 arranged in the front portion of the vehicle compartment 2.

The front fastening portion 34 is configured with a fixing nut (not shown) provided on a side surface of the top portion 42 a on the outer side in the vehicle width direction as a main element. The front fastening portion 34 is fastened and fixed to the mounting bracket 23 (subframe mounting portion) of the corresponding front side frame 7 on the left and right by a bolt 43 (see FIG. 4 and FIG. 6 ). The mounting bracket 23 is formed with a slit 44 (see FIG. 13 ) that opens downward in a fastening wall that is overlapped with the side wall of the top portion 42 a. The bolt 43 is fastened to the fixing nut of the front fastening portion 34 with the shaft portion in a horizontal posture in a state where the shaft portion is inserted through the slit 44. As a result, the front fastening portion 34 of the subframe 8 is fastened and fixed to the corresponding front side frame 7 on the left and right. However, since the fastening wall of the mounting bracket 23 is formed with the slit 44 that opens downward, when an excessive downward relative load acts on the shaft portion of the bolt 43 through the leg portion 42 of the subframe 8, the shaft portion of the bolt 43 slips through the slit 44 and falls downward together with the leg portion 42.

The inclined guide portion 24 of the component mounting bracket 25 described above is arranged on a track in which the top portion 42 a of the leg portion 42 detached from the front side frame 7 is displaced rearward when an impact load is input from the rear of the vehicle. Further, as shown in FIG. 3 , the component mounting bracket 25 is arranged so as to be aligned with the top portion 42 a of the corresponding leg portion 42 on the left and right of the subframe 8 in the vehicle front-rear direction.

FIG. 9 is an enlarged view of the part IX of FIG. 4 with some components removed, and FIG. 10 is an enlarged view of the part X of FIG. 5 . As shown in these drawings, the rear fastening portion 35 of the subframe 8 includes a tubular body 45 through which the bolt 15 penetrates in the vertical direction, and a convex portion 46 protruding from the tubular body toward the vehicle rear side. The rear fastening portion 35 is fixed to the lower end of the mount bracket 13 by the bolt 15 penetrating the support plate 14 at the lower end of the mount bracket 13 and being fastened to the fixing nut 17. In this state, the tip portion of the convex portion 46 directed toward the vehicle rear side faces the inclined guide portion 33 in the front portion of the tunnel frame 11.

The inclined wall 20 of the inclined guide portion 33 faces the convex portion 46 from the vehicle rear side at the position rearward of the fastening portion (fixing nut 17) of the support plate 14. The inclined wall 20 constitutes a fall restricting wall against which the convex portion 46 is pressed from the front when an impact load is input from the front of the vehicle. When an impact load is input, the convex portion 46 is pressed against the front surface of the rear fastening portion 35, so that the falling of the tubular body 45 in the direction in which the tip portion of the convex portion 46 is lifted upward is restricted. The inclined wall 20 constitutes the fall restricting wall that restricts the falling of the tubular body 45.

As shown in FIG. 9 and FIG. 10 , the convex portion 46 of the rear fastening portion 35 includes a contact surface 46 a that comes into contact with the inclined wall 20 which is the fall restricting wall when an impact load is input from the front of the vehicle, and an upper inclined surface 46 b that inclines downward from the upper region of the tubular body 45 toward the vehicle rear side and connects the upper region and the contact surface 46 a.

Further, as shown in FIG. 9 and FIG. 10 , one end portion of a long hinge plate 47 having a U-shaped cross section is fastened and fixed between the lower surface of the tubular body 45 of the rear fastening portion 35 and a head portion 15 a of the bolt 15. The other end portion of the hinge plate 47 is fixed to the lower surface near the front portion of the tunnel frame 11. The hinge plate 47 controls the falling behavior of the subframe 8 when the subframe 8 falls at the time of input of an impact load from the vehicle front side.

FIG. 11 is a perspective view corresponding to the arrow view XI of FIG. 5 . As shown in FIG. 11 , a highly rigid reinforcing plate 48 (reinforcing member) is attached to the rear surface side of the inclined wall 20 (fall restricting wall) in the front portion of the tunnel frame 11. The reinforcing plate 48 has an upper joint portion 48 a joined to the upper surface of the support plate 14, and an inclined portion joint portion 48 b that includes downward from the rear portion of the upper joint portion 48 a toward the vehicle rear side and is joined to the rear surface of the tunnel frame 11.

The upper joint portion 48 a is formed with an elongated hole 49 that surrounds the fixing nut 17 fixed to the upper surface of the support plate 14 and has a gap d between the upper joint portion 48 a and the rear portion of the fixing nut 17. The support plate 14 is joined to the edge portion of the opening 50 at the lower end of the mount bracket 13. The fixing nut 17 fixed on the support plate 14 is arranged close to an edge portion 50 a on the front side of the opening 50.

The inclined portion joint portion 48 b of the reinforcing plate 48 is formed with a reinforcing convex portion 51 that bulges toward the vehicle front side at a position rearward of the inclined wall 20 (fall restricting wall) with which the contact surface 46 a of the convex portion 46 comes into contact when an impact load is input from the front of the vehicle. The reinforcing convex portion 51 supports the inclined wall 20 from the rear side when the convex portion 46 of the rear fastening portion 35 is pressed against the front surface side of the inclined wall 20 at the time of input of an impact load from the front of the vehicle.

In addition, as shown in FIG. 2 and FIG. 5 , the steering gear box 40 mounted on the upper surface on the rear portion side of the subframe 8 has an assist motor 40 a arranged at a portion slightly to the right of the center in the vehicle width direction. The motor 40 a has a relatively large outer diameter, and as shown in FIG. 2 , the motor 40 a bulges to the rearmost upper side in the steering gear box 40. The front surface of an inclined guide portion 60 of the dash lower panel 5 faces the rear side of the motor 40 a. The front surface of the inclined guide portion 60 inclines downward toward the vehicle rear side, and when an impact load is input from the front of the vehicle, the motor 40 a comes into contact with the front surface along with the rearward displacement of the subframe 8. Further, as shown in FIG. 2 , a dash cross member 55 extending along the vehicle width direction is arranged on the rear surface of the dash lower panel 5. The dash cross member 55 is joined to the rear surface position of the inclined guide portion 60 on the rear surface of the dash lower panel 5.

Here, a case of the motor 40 a is formed of a material having higher rigidity than an aluminum casting such as a steel material. That is, the case of the motor 40 a has higher rigidity than the leg portions 42 of the subframe 8 made of an aluminum casting. The front surface of the inclined guide portion 60 of the dash lower panel 5 with which the motor 40 a comes into contact when an impact load is input from the front of the vehicle is set to a gentle downward inclination angle compared with the front surface of the inclined guide portion 24 of the component mounting bracket 25 with which the top portion 42 a of the leg portion 42 comes into contact.

In addition, the front surface of the inclined guide portion 60 of the dash lower panel 5 is arranged to face the rear side of the motor 40 a, and the front surface of the inclined wall 20 in the front portion of the tunnel frame 11 is arranged to face the rear side of the rear fastening portion 35 of the subframe 8. The separation distance between the rear fastening portion 35 and the inclined wall 20 is set shorter than the separation distance between the motor 40 a and the inclined guide portion 60. Further, the separation distance between the top portion 42 a of the leg portion 42 of the subframe 8 and the inclined guide portion 24 of the component mounting bracket 25 is set longer than the separation distance between the motor 40 a and the inclined guide portion 60. Therefore, when an impact load is input from the front of the vehicle, the rear fastening portion 35 comes into contact with the inclined wall 20 first, and then the motor 40 a comes into contact with the inclined guide portion 60, and thereafter the top portion 42 a of the leg portion 42 comes into contact with the inclined guide portion 24.

Subsequently, an example of the deformation behavior of the front portion of the vehicle 1 when an impact load is input from the front surface of the vehicle 1 will be described with reference to FIG. 12 to FIG. 18 . When an impact load is input from the front surface of the vehicle 1, the subframe 8 is pressed toward the vehicle rear side along with the rearward displacement of the power unit such as the engine, and as shown in FIG. 12 , the convex portion 46 of the rear fastening portion 35 of the subframe 8 is pressed against the inclined wall 20 in the front portion of the tunnel frame 11. As a result, the convex portion 46 receives a reaction force from the inclined wall 20, and the falling deformation in which the tubular body 45 of the rear fastening portion 35 is lifted upward is restricted. As a result, out-of-plane deformation of the support plate 14 to which the bolt 15 is fastened is suppressed. When the subframe 8 is further pressed toward the vehicle rear side in this state, the support plate 14 starts to break, and the convex portion 46 of the rear fastening portion 35 is guided rearward and downward along the inclined wall 20.

On the other hand, when an impact load is input from the front surface to the front portion of the front side frame 7, as shown in FIG. 13 , with the bending starting point 22 near the rear portion as the starting point, the front side frame 7 starts to bend and deform so that the front portion of the bending starting point 22 is lifted upward. As a result, the mounting bracket 23 (subframe mounting portion) of the front side frame 7 is lifted upward, while the subframe 8 continues to be pressed toward the vehicle rear side. As a result, the bolt 43 of the front fastening portion 34 is detached downward from the slit 44 of the mounting bracket 23, and the leg portion 42 of the subframe 8 falls downward from the front side frame 7.

Moreover, when the input of the impact load continues, as shown in FIG. 14 , the front fastening portion is completely detached from the mount bracket 13 together with the bolt 15 due to the breakage of the support plate 14, and the motor 40 a on the subframe 8 comes into contact with the inclined guide portion 60 of the dash lower panel 5. As a result, the motor 40 a is guided rearward and downward along the inclined guide portion 60. Further, as shown in FIG. 15 , before and after the contact between the motor 40 a and the inclined guide portion 60, the tubular body 45 of the rear fastening portion 35 comes into contact with the inclined wall 20, and the tubular body 45 is guided rearward and downward along the inclined wall 20.

Thereafter, when the input of the impact load further continues, the entire subframe 8 is displaced rearward while inclining rearward, and as shown in FIG. 17 , the top portion 42 a of the leg portion 42 of the subframe 8 comes into contact with the inclined guide portion 24 of the component mounting bracket 25. As a result, the top portion 42 a of the leg portion 42 is guided rearward and downward along the slope of the inclined guide portion 24. In this way, when the guidance of the leg portion 42 performed by the inclined guide portion 24 is completed, the entire subframe 8 falls below the dash lower panel 5 as shown in FIG. 18 .

As described above, in the front structure of the vehicle body according to the present embodiment, the rear fastening portion 35 of the subframe 7 is provided with the convex portion 46 that protrudes from the tubular body 45 toward the vehicle rear side, and the inclined wall 20 (fall restricting wall) facing the convex portion 46 of the rear fastening portion 35 from the vehicle rear side is provided on the rear side of the fastening portion of the support plate 14 at the lower end of the mount bracket 13. Therefore, when an impact load is input from the front of the vehicle, the convex portion 46 is pressed against the inclined wall 20, so that the falling of the tubular body 45 of the rear fastening portion 35 is restricted, and the out-of-plane deformation of the support plate 14 is suppressed. Accordingly, when the front structure of the vehicle body according to the present embodiment is adopted, the support plate 14 can be reliably broken and the subframe 8 can be dropped downward more smoothly when an impact load is input from the front of the vehicle.

Further, in the front structure of the vehicle body according to the present embodiment, the convex portion 46 of the rear fastening portion 35 is formed with the contact surface 46 a that comes into contact with the inclined wall 20 when an impact load is input from the front of the vehicle, and the upper inclined surface 46 b that inclines downward from the upper region of the tubular body 45 toward the vehicle rear side and connects the upper region and the contact surface 46 a. Therefore, the contact surface 46 a can be arranged at a sufficiently low position at the rear end of the convex portion 46, and the reaction force acting on the contact surface 46 a from the inclined wall 20 can be efficiently transmitted to the tubular body 45 through a portion having a vertical height that gradually increases toward the root portion side (the side of the tubular body 45) of the upper inclined surface 46 b. Accordingly, when this configuration is adopted, the falling of the tubular body 45 of the rear fastening portion 35 at the time of input of an impact load can be reliably restricted and the out-of-plane deformation of the support plate 14 can be further suppressed.

In addition, in the front structure of the vehicle body according to the present embodiment, the highly rigid reinforcing plate 48 is attached to the rear surface side of the inclined wall 20, and the reinforcing convex portion 51 that bulges toward the vehicle front side is provided at the position rearward of the portion, with which the contact surface 46 a of the convex portion 46 comes into contact when an impact load is input from the front of the vehicle, of the reinforcing plate 48. Therefore, when the contact surface 46 a of the convex portion 46 of the rear fastening portion 35 is pressed against the inclined wall 20 at the time of input of an impact load from the front of the vehicle, the reinforcing convex portion 51 of the reinforcing plate 48 arranged on the rear side takes the pressing load thereof. Accordingly, when this configuration is adopted, the reaction force can quickly act on the contact surface 46 a of the convex portion 51, so the falling of the tubular body 45 of the rear fastening portion 35 can be more reliably restricted.

Furthermore, in the front structure of the vehicle body according to the present embodiment, the upper joint portion 48 a of the reinforcing plate 48 is formed with the elongated hole 49 that surrounds the periphery of the fixing nut 17 of the support plate 14 and has the gap d between the upper joint portion 48 a and the rear portion of the fixing nut 17. Therefore, at the time of input of an impact load from the front of the vehicle, when the load toward the vehicle rear side acts on the fixing nut 17 through the bolt 15 along with the rearward displacement of the rear fastening portion 35, the fixing nut 17 is displaced toward the rear of the vehicle in the elongated hole 49 of the reinforcing plate 48 while being pulled downward. Accordingly, when this configuration is adopted, the support plate 17 can be reliably broken and the rear portion of the subframe 8 can be dropped downward when an impact load is input.

Further, in the front structure of the vehicle body according to the present embodiment, the support plate 14 is fixed to the edge portion of the opening 50 at the lower end of the mount bracket 13, and the fixing nut 17 fixed to the support plate 14 is arranged close to the edge portion 50 a on the front side of the opening 50 of the highly rigid mount bracket 13. As a result, the portion of the support plate 14 on the front side of the fixing nut 17 is supported close to the edge portion of the highly rigid opening 50 of the mount bracket 13. Therefore, at the time of input of an impact load from the front of the vehicle, when the load toward the vehicle rear side acts on the fixing nut 17 through the bolt 15 along with the rearward displacement of the rear fastening portion 35, stress tends to concentrate in a narrow range on the rear side of the fixing nut 17 of the support plate 14. Accordingly, when this configuration is adopted, a part of the support plate 14 can be quickly broken and the rear portion of the subframe 8 can be reliably dropped downward when an impact load is input.

In addition, in the front structure of the vehicle body according to the present embodiment, the step portion 21 which includes the front wall 18 extending downward from the lower end of the mount bracket 13, the substantially horizontal wall 19 extending toward the rear of the vehicle from the lower end of the front wall 18, and the inclined wall 20 inclining downward from the rear end of the substantially horizontal wall 19 toward the vehicle rear side is provided at the rear portion of the support plate 14, and the inclined wall 20 is used as the fall restricting wall. Therefore, when an impact load is input from the front of the vehicle, the convex portion 46 protruding from the rear fastening portion 35 comes into contact with the inclined wall 20 of the step portion 21, so that the falling of the tubular body 45 of the rear fastening portion 35 can be restricted. Further, even if the convex portion 46 may be slightly lifted upward due to the falling load of the tubular body 45, the convex portion 46 comes into contact with the substantially horizontal wall 19 of the step portion 21, so that the falling of the tubular body 45 can be reliably restricted. In addition, after the fastening plate 14 breaks and the rear fastening portion 35 is detached from the mount bracket 13, the tubular body 45 of the rear fastening portion 35 can be guided by the front surface side of the step portion 21 and smoothly dropped downward.

Furthermore, in the front structure of the vehicle body according to the present embodiment, since the step portion 21 is formed at the front end portion of the tunnel frame 11 that extends in the vehicle front-rear direction below the vehicle compartment 2, when an impact load is input from the front of the vehicle, the rear fastening portion 35 detached from the mount bracket 13 can be smoothly dropped downward along the front surface of the step portion 21 and the lower surface of the tunnel frame 11.

Further, in the front structure of the vehicle body according to the present embodiment, the inclined guide portion 60 that inclines downward toward the vehicle rear side is provided at a position, which faces the upper portion (motor 40 a) of the steering gear box 40 from the vehicle rear side, of the dash lower panel 5. Therefore, when the subframe 8 is displaced rearward at the time of input of an impact load from the front of the vehicle, the upper portion of the steering gear box 40 can be guided rearward and downward along the inclined guide portion 60 of the dash lower panel 5. Accordingly, when this configuration is adopted, the subframe 8 can be dropped downward more smoothly.

In addition, in the front structure of the vehicle body according to the present embodiment, since the inclined guide portion 60 of the dash lower panel 5 is arranged on the inner side in the vehicle width direction of the front end portion of the tunnel frame 11, when an impact load is input from the front of the vehicle, the subframe 8 can be stably dropped downward along the inclined guide portion 60 of the dash lower panel 5 and the step portion 21 at the front end of the tunnel frame 11.

Furthermore, in the front structure of the vehicle body according to the present embodiment, the component mounting bracket 25 having the inclined guide portion 24 (inclined portion) with a front surface that inclines downward toward the vehicle rear side is coupled to the rear portion of the front side frame 7, and the inclined guide portion 24 is arranged on a track in which the front fastening portion 34 (the top portion 42 a of the leg portion 42) detached from the front side frame 7 is displaced rearward when an impact load is input from the front of the vehicle. Therefore, when an impact load is input from the front of the vehicle, the front fastening portion 34 detached from the front side frame 7 comes into contact with the inclined guide portion 24 on the component mounting bracket 25, so that the front portion of the front side frame 7 can be smoothly guided to rearward and downward.

Nevertheless, the disclosure is not limited to the above embodiment, and various design changes can be made without departing from the gist thereof. 

What is claimed is:
 1. A front structure of a vehicle body, comprising: a pair of left and right front side frames extending to a front of a vehicle on a front side of a vehicle compartment; a subframe erected below the pair of front side frames; and a vehicle compartment front structure body arranged in a front portion of the vehicle compartment, wherein the subframe comprises: a subframe body supporting a mounted component; and a rear fastening portion fastened to the vehicle compartment front structure body in a rear region of the subframe body, wherein the rear fastening portion comprises: a tubular body through which a bolt penetrates in a vertical direction; and a convex portion which protrudes from the tubular body to a vehicle rear side, wherein the vehicle compartment front structure body comprises: a support plate extending substantially horizontally in which the tubular body is fastened to a lower surface of the support plate by the bolt; and a fall restricting wall which faces the convex portion from the vehicle rear side at a position rearward of a fastening portion of the support plate fastened with the bolt and against which the convex portion is pressed when an impact load is input from the front of the vehicle, and wherein a reinforcing member having a high rigidity is attached to a rear surface side of the fall restricting wall, and a reinforcing convex portion is provided that bulges toward a vehicle front side and supports the fall restricting wall from the vehicle rear side when the convex portion is pressed against the fall restricting wall.
 2. The front structure of the vehicle body according to claim 1, wherein the reinforcing member has an upper joint portion joined to an upper surface of the support plate, a fixing nut constituting the fastening portion is fixed to the upper surface of the support plate, and the upper joint portion is formed with an elongated hole that surrounds a periphery of the fixing nut and has a gap between the upper joint portion and a rear portion of the fixing nut.
 3. A front structure of a vehicle body, comprising: a pair of left and right front side frames extending to a front of a vehicle on a front side of a vehicle compartment; a subframe erected below the pair of front side frames; and a vehicle compartment front structure body arranged in a front portion of the vehicle compartment, wherein the subframe comprises: a subframe body supporting a mounted component; and a rear fastening portion fastened to the vehicle compartment front structure body in a rear region of the subframe body, wherein the rear fastening portion comprises: a tubular body through which a bolt penetrates in a vertical direction; and a convex portion which protrudes from the tubular body to a vehicle rear side, wherein the vehicle compartment front structure body comprises: a support plate extending substantially horizontally in which the tubular body is fastened to a lower surface of the support plate by the bolt; and a fall restricting wall which faces the convex portion from the vehicle rear side at a position rearward of a fastening portion of the support plate fastened with the bolt and against which the convex portion is pressed when an impact load is input from the front of the vehicle, wherein a step portion comprising a front wall extending downward from the lower end of the mount bracket, a substantially horizontal wall extending from a lower end of the front wall to a rear of the vehicle, and an inclined wall inclining downward from a rear end of the substantially horizontal wall toward the vehicle rear side is provided at a rear portion of the support plate, and the inclined wall serves as the fall restricting wall.
 4. The front structure of the vehicle body according to claim 3, wherein a tunnel frame extending in a vehicle front-rear direction is arranged below the vehicle compartment, and the step portion is arranged at a front end portion of the tunnel frame.
 5. The front structure of the vehicle body according to claim 4, wherein a steering gear box is mounted on the subframe so as to project upward, the vehicle compartment front structure body comprises a dash lower panel that separates the vehicle compartment and a front compartment on a front side of the vehicle compartment, and an inclined guide portion that inclines downward toward the vehicle rear side is provided at a position, which faces an upper portion of the steering gear box from the vehicle rear side, of the dash lower panel.
 6. The front structure of the vehicle body according to claim 5, wherein the inclined guide portion of the dash lower panel is arranged on an inner side in a vehicle width direction of the front end portion of the tunnel frame.
 7. The front structure of the vehicle body according to claim 6, wherein the subframe comprises a front fastening portion fastened to the front side frame in the front region of the subframe body, a component mounting bracket having an inclined portion with a front surface that inclines downward toward the vehicle rear side is coupled to a rear portion of each of the front side frames, and the inclined portion is arranged on a track in which the front fastening portion detached from the front side frame is displaced rearward when the impact load is input from the front of the vehicle. 